Testing a Role of Vertical Mixing in Abrupt Climate Change

测试垂直混合在气候突变中的作用

• 批准号: 0602230
• 负责人: Olivier Marchal
• 金额: $ 33.75万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-15 至 2009-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0602230&HistoricalAwards=false
• 关键词: Testing; Role; Vertical; Mixing; Abrupt

Testing a Role of Vertical Mixing in Abrupt Climate ChangeOlivier MarchalThe meridional overturning circulation (MOC) of the ocean is viewed as an important component of the climate system owing to its attendant poleward heat flux. A popular theory ascribes rapid climate changes of the geological past to variations in the MOC caused by glacial meltwater input to the northern North Atlantic. The theory, however, is currently challenged by studies based on idealized models, showing that the response of the MOC to surface forcing depends qualitatively on the representation of vertical mixing in the models: if the mixing is represented with a fixed, apparent diffusivity, the MOC decreases with decreased equator-to-pole density contrast at the surface (the usual result), whereas if the diffusivity depends on vertical density stratification (perhaps a more plausible assumption), the MOC increases with decreased density contrast. Here we will determine whether a similar result holds for the time-dependent response of the circulation to surface freshening in a realistic model of the global ocean. To meet our goal we will conduct a set of numerical experiments with an ocean general circulation model, which rely on different assumptions about vertical mixing, and compare their results with paleoceanographic data obtained from sediments. Our work plan includes three major tasks.First, the model will be set up to represent the global ocean with realistic bathymetry. Second, a series of model equilibrium states assuming constant or stability-dependent vertical diffusivity will be generated. Third, these states will be perturbed by applying an anomaly in the surface freshwater flux. Comparing results obtained from different assumptions about vertical mixing will provide a test of our hypothesis. Comparing model results with paleoceanographic data will enable us to assess the extent to which these data could contribute to an outstanding question in physical oceanography, related to the role of vertical mixing in the MOC.

测试垂直混合在突然的气候变化中的作用Marchal，由于其随之而来的极点热通量，海洋的子午倾覆循环（MOC）被视为气候系统的重要组成部分。一种流行的理论将地质过去的气候变化归因于北大西洋北部冰川融水引起的MOC的变化。然而，该理论目前受到基于理想化模型的研究的挑战，表明MOC对表面强迫的响应在定性上取决于模型中垂直混合的表示：如果以固定的，明显的扩散率表示混合，则MOC随着表面的赤道对极密度对比而降低（通常的结果），而如果扩散率取决于垂直密度分层（也许是一个更合理的假设），则MOC随密度对比度降低而增加。在这里，我们将确定在全球海洋现实模型中循环对循环表面鲜明的时间依赖性响应是否存在。为了实现我们的目标，我们将使用海洋一般循环模型进行一系列数值实验，该模型依赖于垂直混合的不同假设，并将其结果与从沉积物获得的古环摄影数据进行比较。我们的工作计划包括三个重大任务。首先，该模型将通过逼真的测深度代表全球海洋。其次，假设将产生恒定或稳定性垂直扩散率的一系列模型平衡状态。第三，这些状态将通过在地表淡水通量中施加异常来扰动。比较从垂直混合的不同假设获得的结果将提供我们假设的检验。将模型结果与古环学数据进行比较将使我们能够评估这些数据在多大程度上促成了与垂直混合在MOC中的作用有关的物理海洋学中出色问题的程度。